The invention relates to an apparatus for supplying an electric consumer with a high DC voltage from a DC voltage source with positive and negative output potential relatively to earth potential, comprising an evaluating circuit which has its own operating voltage source between a current supply connection and a reference potential line and to which a measuring signal can be fed depending on the consumer voltage and/or the consumer current and which compares the measuring signal with a predetermined value and, depending on the result of the comparison, feeds a control signal by way of a separating stage to a setter influencing the consumer voltage, wherein the evaluating circuit has an operational amplifier for each measuring signal input, one input of the amplifier being preceded by a series resistor and the other input being connected to the reference potential line.